1. Field of the Invention
This invention relates generally to electronic test and monitoring equipment and more particularly to voltage level monitoring equipment.
2. Description of the Prior Art
Battery level indicators are well known in the prior art. For example, in U.S. Pat. No. 4,020,414 of Paredes, a battery-status indicator includes a plurality of comparators having one of their inputs coupled to a reference voltage through a zener diode 56 and having their other input coupled to a battery through a resistive scaling network. The outputs of three of the comparators are coupled to light bulbs 74-78 through driving transistors 80-84, and the output of the fourth comparators is coupled to an alarm 86 by a driving transistor 88. The lights 74-78 will light in sequence as the voltage level drops until the alarm 86 finally sounds.
A problem with battery voltage indicators such as those taught by Paredes is that they drain a substantial amount of current from the battery when two or more of the indicating lights are lit. Furthermore, the display is confusing since a plurality of indicator lights can be illuminated at one time.
A disadvantage with most battery voltage indicators is that they are either of the under-voltage or the over-voltage type. For example, Peredes is an under-voltage type indicator which does not detect or display a warning when dangerous over voltage conditions occur. What the prior art fails to disclose, then, is a ranged voltage monitor which sounds an alarm when the voltage either falls below the predetermined level or rises above a predetermined level, and which accurately and efficiently displays the voltage level within the range.